Apple is trying to boost the iPad, so obviously they're playing up it's future role and persuading people it's the next big thing. What else does anyone expect them to do?
I think Apple genuinely do think iOS is the future of mainstream consumer computing, and a big chunk of professional computing as well. But that doesn't mean OSX has no future. Nor does it mean this future of computing is going to be here in full force and sweep traditional form factors under the rug in the next 6 months. But 5 or 10 years down the line? Maybe. But that's not a concern if you're buying a machine today.
Apple makes plenty of profit from its OSX machines, and needs to diversify more, not less. It also needs powerful machines for development, design and other tasks. Apple's culture would never accept switching to Windows, and Linux is still lacking in too many respects.
What Apple should do is improve OSX (high color depth support, better graphics performance, ultra low latency etc.) as well as releasing cutting edge hardware that outperforms anything in the industry. Rackable, higher-end Mac Pros supporting SLI and gobs of memory that could gang together using Thunderbolt would be a good start. Apple should be using its vast market capitalization to lead the industry forward. It has the resources to do many things at once.
iPads are far from a replacement for your MacBook or iMac - for one you can't properly multitask, and you as a developer you couldn't properly debug and write code on an iPad.
OSX will be around for years to come.
I do not see the death of OS X on iOS. If anything, I see it morphing.